The present invention relates an operation speed measuring circuit and a semiconductor device incorporating this circuit and, more particularly, to an operation speed measuring circuit suited to measure an operation speed in order to assure an operation of a semiconductor integrated circuit.
Existing and prospective semiconductor makers are required to develop and offer an IC having functions or circuits responding to demands of individual users for short period of time.
In the case of responding to such requests, the makers inevitably need a small quantity of but multiple kinds of productions, and this in turn requires a manufacturing system capable of facilitating a design and providing a flexible respondency. Aiming at this, the preparation for an environment of DA (Design Automation) is being advanced such as preparing the cell library.
At present, with an advancement and the spread of the designing system, the user is able to independently design the IC, and consequently there is an increasing tendency of decentralization into a designer and a manufacturer. If the user designs the IC and orders the maker to manufacture it, the user transfers date about the design to the maker. The maker completes the design on the basis of the data, prepares a mask and manufactures the IC.
There is an IC known as ASIC (Application-Specific IC) among the ICs each constructed by integrating functions necessary for a specific application required by the user.
Given that typical ABICS are a gate array in which elements are regularly arranged independently of a kind-of-chip design with the LSI and a standard cell for forming an LSI chip by hierarchically stacking standardized cell groups registered beforehand and by performing laying out the cell groups and wirings.
A semicustom IC is an IC in which the function needed by a specific user is realized by use of a short-term development type designing element such as the gate array, the standard cell, etc.
The semicustom IC completed with an order received from the user has to be tested for measuring a given performance before being delivered.
A clock frequency of the IC that is dominant at present is a very high as 60-100 MHz, and hence an existing tester is incapable of effecting an operating simulation of the IC.
Under such circumstances, there is used a method of assuring a performance of the IC as a whole by incorporating an operation speed measuring circuit into the IC, measuring an operation speed of the element in this circuit and confirming that a specified operation speed is obtained.
The following is an explanation of how the operation speed measuring circuit is incorporated into the chip.
FIG. 7 is a plan view illustrating an example where the semicustom IC of the conventional operation speed measuring circuit is incorporated into the IC chip. As known from FIG. 7, in the conventional semicustom IC, spaces 70a in the vicinities of four corners of a chip 70 are nothing but empty areas because of being incapable of arranging the wires with respect to an integrated circuit design area 75 at the central portion even when placing an element such as an I/O cell, etc.
Accordingly, an operation speed measuring circuit 71 is so constructed as to be incorporated in a side-by-side relationship within the same area 75 as a specific-application circuit designed by the user. An input cell 72, an output cell 73 and a control cell 74 are connected to the operation speed measuring circuit 71, thereby performing control and input/output operations from outside of the chip.
There arises, however, a problem inherent in the conventional semicustom IC, wherein both the number of gates required and the number of signal pins required increases, and this brings about a rise in the size of the chip because of such a construction that the operation speed measuring circuit is incorporated in the side-by-side relationship within the same area as the specific-application circuit designed by the user as explained above.
Whereas if the size of the chip is fixed, the numbers of the gates and of signal pins that are required for incorporating the operation speed measuring circuit have to be secured previously, and, therefore, a degree of freedom on the occasion of the user's designing the specific-application circuit is remakably restricted.